Dan Walsh's Blog

Got SELinux?

SELinux Enhancements.SELinux policy package now includes a pre-built policy that will only rebuild policy if any customizations have been made. A sample test run shows 4 times speedup on installing the package from 48 Seconds to 12 Seconds and max memory usage from 38M to 6M. In addition to that, SELinux file name transition allows better policy management. For instance, policy writers can take advantage of this and write a policy rule that states, if a SELinux unconfined process creates a file named resolv.conf in a directory labelled etc_t, the file should get labeled appropriately. This results is less chances of mislabeled files. Also, from this release onwards, selinuxfs is mounted at /sys/fs/selinux instead of in /selinux. All the affected components including anaconda, dracut, livecd-tools and policycoreutils have been modified to work with this change.

Pre-Built Policy

We made major changes to the selinux-policy-TYPE rpm. (selinux-policy-targeted-3.10.0-21.fc16)

The rpm now includes a pre-built /etc/selinux/targeted/policy/policy.26. This policy file can be loaded right away in a fresh install. In all previous versions of SELinux for RHEL and Fedora, we rebuilt this file in the post install. The reason for this is we need to recompile in local customizations that the user/administrator might have made on your system. Additionally if any package shipped with a policy we would need to recompile in those policy packages. But as the size of policy grew we were seeing Anaconda installation times grow and memory requirements grow because of selinux-policy package. We were even seeing virtual machine installations blow up on selinux-policy package installs because of limited memory. When we looked at the problem, we realized that on initial install of policy, no user would have made local customizations and very few packages are shipping with their own policy.

I reworked the tools to include the policy packages within the payload and now the package will check in the pre-install if there was any local customizations, if yes, the post install will recompile the policy, but if not the policy will just install.

We also used to have to ship all of the policy modules, over 300, in the directory /usr/share/selinux/targeted and these would be copied into /etc/selinux/targeted/modules/active/, were we would never touch the files in /usr/share/selinux/targeted again. Now we install directly into /etc/selinux/targeted/modules/active/.

What you should see is faster initial installs and faster selinux-package updates. In Fedora 15 a policy-package update would take around 45-50 seconds, in Fedora 16 on an unmodified selinux-policy system it should take < 15 seconds. If you are updating from Fedora 15 the first time, it will still take a long time, but the next update should go quick. If you have modified the SELinux system by adding ppfiles you will still see the recompile times that you always have. :^(